The MicroZOTL circuit was born in 2000 as a showcase for the newly invented ZOTL output stage. It was designed to be simple, small, and to sound incredible.

When LTA reintroduced it in 2015 we added preamp outputs and realized that every system we listened to sounded better with the MicroZOTL in the chain. This led to the creation of our reference MicroZOTL Preamplifier.

• Overbuilt linear power supply: Custom, center-potted toroidal transformer with separate windings for the analog and digital sections of the circuit; extremely low-noise Belleson regulator designed for audio with low output impedance, high bandwidth, and excellent transient response; over 100,000uF of storage capacitance, more than is typically found in power amplifiers.

• Ceramic circuit boards: Comparing ceramic PCBs to standard materials is similar to comparing different insulation material used for wire. Most standard wire uses PVC, while higher performance wire uses a fluoropolymer like PTFE. Ceramic PCBs have a lower dielectric constant and absorb less energy from the signal, which gives better clarity and detail.

• Optimized preamplifier output: The preamp and headphone outputs were given separate coupling components, allowing us to use components ideally suited to each and maintain the excellent headphone amplifier performance of the MicroZOTL.

• High-resolution volume attenuator with integrated balance control: An 8-bit relay-based stepped attenuator gives 0.5dB steps for precise level adjustments. Each channel is independently controlled, so balance adjustments can be made with no additional circuitry or degradation of the sound. With adjustable gain and step settings, each input can be configured to be most usable with a given source.

• Transformer-coupled balanced inputs: To take full advantage of balanced sources we offer optional Lundahl input transformers on the XLR inputs.

• Elegant, North American-made chassis: The casework is designed by award-winning, Richmond, VA-based Fern & Roby.

As other LTA product development brought advances in performance, a foundational change was required to enable the MicroZOTL Preamplifier to keep up. For Level 3 we completely redid the audio section: redesigning the boards, redrawing the layout, re-evaluating components, and improving the circuit.

Using a single larger circuit board instead of several smaller ones let us significantly shorten the signal path and reduce the number of interconnections, which removes opportunities for noise to enter the circuit. Combining the boards also meant that more of the signal path travels on the ceramic PCB. A larger board also gives us enough room to use the best quality components and optimize their placement. Improving the grounding scheme resulted in our quietest preamplifier yet. 

Building on what we’ve learned with the Velo and Aero, the power stage in the preamp was fully reworked to decrease noise and increase output capability. Shared sections of the circuit are separated to give isolated, dedicated power to each output channel. The total power storage increased by 70%, to over 200,000uF, with significantly more of that providing instantaneous power delivery right next to the parts that need it.

By redesigning our custom components and utilizing surface-mount parts in critical areas, the ZOTL stage achieves higher performance.

We’ve also added a high voltage delay and a soft-start filament circuit to warm up the tubes more gently.

Amplifier class: Class A, no feedback

Inputs: 4 Stereo RCA single ended inputs using high quality Cardas connectors; 1 XLR transformer-coupled balanced input, with Lundahl transformers. One Tape input.

Outputs: Headphone ¼” Phone jack, dual RCA single-ended preamplifier outputs, Tape Monitor output

Volume Control: Stepped attenuator with two settings. Default: 100 steps logarithmic; High-Res: 199-steps, linear

Gain: +14dB.

Input sensitivity: 0.75Vrms.

Input impedance: Single-ended: 50k ohms, Balanced: 100k ohms. 

Output impedance: Preamp output: 50 ohms, Headphone output: 1.38 ohm.

Frequency response: -0.06dB/+0.1dB from 20Hz to 20kHz, -3dB at 1.6Hz to 110kHz

THD+N: 0.2% at 1Vrms output, 0.43% at 2Vrms output. 

Crosstalk: -65dB at 1kHz.

Hum+noise: Under -110dB at 2Vrms output. 

Power output: into 15 Ohms: 580mW, 30 Ohms: 300mW

Power consumption: ~50W.

Tube complement: 2 NOS 12AT7 input tubes, two NOS 12SN7 output tubes. 

Dimensions: 17 inches (43.2 cm) wide, 4.2 inches (10.7 cm) tall, 12.4 inches (31.5 cm) deep (including knob and connectors)

Weight: 14 lbs. (6.35 kg.) Shipping weight: 22 lbs. (10 kg)